Method for transmitting and receiving random access request and transmitting and receiving random access response

ABSTRACT

A base station transmits a random access response in response to a random access request (random access preamble) of a user equipment. The random access response includes information about a time when the random access request is transmitted and sequence number information of the random access request (random access preamble). The user equipment checks whether the received random access response is the response of the random access request transmitted by the user equipment, using the information about the time when the random access request transmitted and the sequence number information included in the received random access response.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/340,447 filed on Dec. 29, 2011, which is a continuation of U.S.patent application Ser. No. 12/347,352, filed on Dec. 31, 2008, whichclaims priority of Korean patent application number 10-2008-0047656,filed on May 22, 2008 and U.S. Provisional Application No. 61/018,492,filed on Jan. 1, 2008. The disclosure of each of the foregoingapplications is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wideband radio access system, andmore particularly, to a method of transmitting and receiving a randomaccess request (random access preamble) and transmitting and receiving arandom access response in a wideband radio access system.

2. Discussion of the Related Art

In a technology related to a wideband radio access system, each userequipment may attempt to access the system with a randomly selectedsequence or opportunity in each random access channel (RACH) slot. Abase station detects a random access sequence (or an RACH sequence) andthen transmits a random access response (or an RACH response). Each userequipment receives the random access response from the base station,considers a response including its sequence as its response, andperforms a timing advance operation.

In the technology of this field, each user equipment may attempt toaccess the system with a randomly selected sequence or opportunity ineach RACH slot. A base station detects the RACH sequence and thentransmits a response thereof. Each user equipment receives the RACHresponse from the base station, considers a response including, itssequence as its response and performs a timing advance operation. Atthis time, if an accurate time interval is not present when each userequipment waits for the response, each user equipment may erroneouslyreceive a response of another user equipment as its response. This stateis shown in FIG. 1A. FIG. 1A is a view showing an example of an RACHresponse (random access response). This state may appear in all RACHperiods. Referring to “3GPP TS 36.211 v.8.1.0, ‘Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical channels and modulation’,2007 Dec. 20” regarding to random access in a wideband radio accesssystem, a table for a random access preamble format, a random accesspreamble parameter and random access preamble timing for preambleformats 0 to 3 is described. FIG. 1A shows an RACH slot having a periodof 1 ms and a preamble format of 0.

In FIG. 1A, a first user equipment 1 attempts access with a randomlyselected sequence 1 in an uplink (UL) subframe 0 (S110). In an uplinksubframe 1, a second user equipment 2 attempts access with a randomlyselected sequence 1 (S120). If a base station detects the sequences ofthe two user equipments, the base station transmits responses of thedetected sequences (S130). At this time, the two user equipments 1 and 2which attempt access wait for their responses. When the response of thesequence 1 is reached in an uplink subframe 7, both the user equipment 1(UE1) and the user equipment 2 (UE2) may determine that the responsereached in the uplink subframe 7 is the response for their sequence. Inthis case, one of the two user equipments erroneously determines thatthe response reached in the uplink subframe 7 is its response. Since thetwo user equipments perform time synchronization by the responsereceived in the uplink subframe 7, one user equipment performs erroneoustime synchronization. In addition, since data or a control signal istransmitted again in uplink using the same resource indicated by theresponse, a problem that the two user equipments use the same resourceoccurs.

In FIG. 1 and the description related to FIG. 1, a cell radius is notconsidered in order to facilitate the understanding of the problems ofthe technology related to the present invention. However, if the cellradius is actually about 50 km and the propagation speed of anelectromagnetic wave is considered, a random access preamble transmittedby the user equipment 1 in the uplink subframe 0 may reach the basestation in a downlink subframe 0 or a downlink subframe 1, and a randomaccess preamble transmitted by the user equipment 2 in the uplinksubframe 1 may reach the base station in a downlink subframe 1 or adownlink subframe 2. In addition, a random access response transmittedby the base station in the downlink subframe 1 may reach the userequipment 1 and/or the user equipment 2 in the uplink subframe 1 or anuplink subframe 2 and a random access response transmitted by the basestation in the downlink subframe 2 may reach the user equipment 1 and/orthe user equipment 2 in the uplink subframe 2 or an uplink subframe 3(see FIG. 1B).

Unlike the above example, if a resource available in a time domain inwhich the base station transmits the response is not present, a problemthat the response cannot be transmitted on time occurs. In this case,the response of the RACH slot is not transmitted or is delayed. At thistime there is a need for a method of distinguishing between a delayedresponse and a response which is transmitted on time or between delayedresponses.

In addition, if responses of several RACH slots are collected and aresimultaneously transmitted, there is a need for a method ofdistinguishing between RACH slots.

SUMMARY OF THE INVENTION

An object of the present invention devised to solve the problem lies ona method of transmitting and receiving a random access response, whichis capable of preventing a user equipment which attempts to accessusing, a randomly selected sequence from erroneously receiving aresponse for the access of another user equipment, which attempts accesswith the same sequence, as a response for its access.

The object of the present invention can be achieved by providing amethod of transmitting a random access preamble and receiving a randomaccess response, the method including: at an user equipment,transmitting the tandem access preamble; and at the user equipment,receiving the random access response of the random access preamble,wherein the random access response received by the user equipmentincludes time related information of a time point when the random accesspreamble corresponding to the received random access response istransmitted. The time related information may include a subframe relatednumber at the time point when the user equipment transmits the randomaccess preamble. The subframe related number may be a number allocatedto a subframe, in which a random access channel (RACH) slot is present,of subframes. The allocation may be performed by a modulo operation ofthe subframe number, in which the RACH slot is present, of thesubframes. The modulo operation may be a modulo-4 operation. The timerelated information may be estimated on the basis of a cell size.

In another aspect of the present invention, provided herein is a methodof receiving a random access preamble and transmitting a random accessresponse, the method including: at a base station, receiving the randomaccess preamble; and at the base station, transmitting the random accessresponse of the received random access preamble, wherein the transmittedrandom access response includes time related information of a time pointwhen the received random access preamble is transmitted or delay offsetinformation related to a processing delay time consumed for transmittingthe random access response from when the base station receives therandom access preamble. The transmitted time point may be estimated bythe base station on the basis of a cell size. The received random accesspreamble may include time related information of the time point when thereceived random access preamble is transmitted, and the time relatedinformation included in the transmitted random access response may beassociated with time related information included in the received randomaccess request.

In another aspect of the present invention, provided herein is method oftransmitting a random access preamble and receiving a random accessresponse, the method including: at a user equipment, transmitting therandom access preamble; and at the user equipment, receiving the randomaccess response, wherein the receiving of the random access response atthe user equipment is performed in a predetermined time period includinga predetermined time after a time point when the random access preambleis transmitted, and the predetermined time is a time when a timeobtained by adding a predetermined offset time to a time correspondingto a half of a hybrid automatic repeat request (HARQ) process round triptime elapses after the time point when the random access preamble istransmitted. The random access response may include delay offsetinformation, and the delay offset information may be used to change thepredetermined time period.

According to the present invention, it is possible to solve a problemthat a user equipment recognizes a random access response for a randomaccess request transmitted by another user equipment as a response forits random access request.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIGS. 1A and 1B are views showing an example of a random accessresponse.

FIG. 2A is a view showing an example of a frame structure used in awideband radio access system.

FIG. 2B is a view showing an example of a random access preamble format.

FIGS. 3A and 3B are views showing a random access response includingtime information according to an embodiment of the present invention.

FIG. 4 is a flowchart illustrating a method of transmitting andreceiving a random access request and a random access response accordingto another embodiment of the present invention.

FIGS. 5A and 5B are views showing a random access response includingtime information if an RACH slot has a period of 2 ms, according toanother embodiment of the present invention.

FIGS. 6A and 6B are views showing a delayed random access response if anRACH slot has a period of 2 ms, according to the embodiment of thepresent invention.

FIGS. 7A and 7B are views explaining renumbering and grouping accordingto another embodiment of the present invention.

FIG. 8 is a flowchart in detail illustrating an internal process of astep S420 of FIG. 4 according to another embodiment of the presentinvention.

FIG. 9 is a flowchart illustrating a method of transmitting andreceiving a random access request and a random access response accordingto another embodiment of the present invention.

FIG. 10 is a view in detail showing an internal process of a step S920(S920′) of FIG. 9.

FIG. 11 is a view explaining the principle of an automatic repeatrequest (ARQ).

FIG. 12 is a view explaining the principle of a hybrid automatic repeatrequest (HARQ).

FIG. 13 is a view showing a detailed, example of a HARQ processaccording to another embodiment of the present invention.

FIG. 14 is a flowchart illustrating a method of transmitting andreceiving a random access request and a random access response accordingto another embodiment of the present invention.

FIG. 15 is a view explaining the classification of channels according tolayers in a wideband radio access system.

FIG. 16 is a view explaining the classification of channels according tolayers and areas.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invent in, examples of which are illustrated in the accompanyingdrawings. The following embodiments are examples applied to a widebandradio access system, which may refer to “3GPP TS 36.211 v.8.1.0,‘Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channelsand modulation’, 2007 Dec. 20” regarding to random access in a widebandradio access system.

In the wideband radio access system, a “channel” refers to a passageallocated to transmitter and receiver and indicates a logical signalpassage rather than a physical transmission path. Accordingly, severalchannels may exist in one transmission path.

In an asynchronous wideband code division multiplexing access (WCDMA),three channels are defined according to layers. A first channel is alogical channel between a radio link control (RLC) layer and a mediumaccess control (MAC) layer, and is classified depending on which type ofinformation is included, that is, the “type of information”. A secondtransport channel is a channel between the MAC layer and a physicallayer, is classified according to the “characteristics of deliveryinformation”, and is largely classified into a dedicated transportchannel and a common transport channel. A third physical channel is achannel transmitted via an actual antenna and is classified according tothe “radio resource and, more particularly, efficiency of a code and RIoutput” (see FIGS. 15 and 16). In the RLC layer for providing transportreliability, retransmission is performed in the unit of logicalchannels. That is, when an error occurs in a receiver side, logicalchannel retransmission is performed in the information units(transmission time intervals (TTIs)), instead of the frame unitsconfigured in the physical layer.

The transport channel is the delivery channel between the physical layerand an upper layer and is defined according to the characteristics oftransport data and transmitting methods. The transport channel transmitsdata received from the logical channel, but the logical channel and thetransport channel do not one-to-one correspond to each other. Severallogical channels may be transmitted using one transport channel.Accordingly, the MAC layer between the logical channel and the transportchannel perform mapping between the logical channel and the transportchannel.

Similar to the logical channel, the transport channel is considered asthe flow of data rather than the physical channel. In particular, sinceall protocols are located at the same location in the user equipment,the transport channel of the user equipment is internally definedbetween the MAC layer and the physical layer. Since the physical layeris located at a node B in a universal mobile telecommunication system(UMTS) terrestrial radio access network (UTRAN), an appropriateinterface should be defined for data exchange with the MAC layer locatedat a radio network controller (RNC).

The transport channel is classified into the dedicated transport channeland the common transport channel according to the characteristics of thedelivery information. A dedicated channel (DCH) belongs to the dedicatedtransport channel, and a broadcasting channel (BCH) a forward accesschannel (FACH), a paging channel (PCH) a random access channel (RACH), adownlink shared channel (DSCH), a common packet channel (CPCH), and ahigh speed-downlink shared channel (HS-DSCH) belong to the commontransport channel.

The RACH transmits control information such as short packet data such asa short messaging service (SMS) and call set-up in uplink, and operatesby a process similar to a synchronous random access channel on the basisof a slotted ALOHA random access scheme. Accordingly, collision riskwith the signal of another user equipment may occur, and an open-looppower control is used. While a transmission rate of 9.6 kbps is definedin the synchronous CDMA system, a transmission rate of up to 120 kbps isdefined in an asynchronous system. However, the transmission rate isactually restricted to about 15 kbps.

The physical channel is transmitted via the actual antenna and varioustypes of information are transmitted is one physical channel or severalphysical channels. Since same overhead physical channels are used foraiding the transmission and reception of the physical channelsregardless of the upper layer, they are generated by a base stationwithout a direct mapping relation with the transport channel. Among thetransport channels, the RACH is mapped to a physical random accesschannel (PRACH) of the physical channel.

In uplink random access, a user equipment which does not access a basestation uses a slotted ALOHA random access scheme in order to access thebase station, and gradually increases and repeatedly transmits a probeoutput until access becomes successful when a probe (an action forchecking and finding something) transmission fails. In the WCDMA system,an Acquisition Indication sense multiple access (AiSMA) scheme oftransmitting only a preamble part in each probe, receiving informationthat synchronization acquisition of an access preamble is performed fromthe base station via an acquisition indicated on channel (AICH) andtransmitting a message part is employed. Accordingly, since thetransmission time of the random access probe in the WCDMA system isextremely shorter than that of the synchronous system, a base stationreception noise phenomenon due to the probes which fail in the access tothe base station is remarkably improved. Information about subgroups andcodes available for a random access preamble part is specified accordingto access service rating via a system information block (SIB) 5 messagefrom a radio resource management layer which is an upper layer, andinformation about a transmission format of a message part and a systemframe number is received from the MAC layer. A random access channel isused to perform an operation related to a request for the set-up of thecall to the base station and to transmit short one-way packet data ofone or two frames in uplink.

The message part transmitted after an ACK signal for a preamble signalis received has a length of 10 msec or 20 msec, and a substantial datapart and a control part are multiplexed to an I/Q channel, areBPSK-modulated and are simultaneously transmitted.

In order to minimize a probability that RACH signals of several userequipments collide, the transmission of the RACH signals is started inrespective access slots specified to the user equipments. The accessslot number is uniquely specified in an upper layer. Parameters relatedto the RACH are broadcasted to all the reception-standby user equipmentsvia the SIB 5 of the BCH.

FIG. 2A is a view showing an example of a frame structure used in awideband radio access system.

In “3GPP TS 36.211 v.8.1.0, ‘Evolved Universal Terrestrial Radio Access(E-UTRA); Physical channels and modulation’, 2007 Dec. 20”, a physicalchannel for an evolved UTRA is described. Two frame structures may beused. A first frame structure (see FIG. 2A) is applicable to a fullduplex frequency division duplex (FDD) and a half duplex FDD. Each radioframe has a length of 10 ms and is configured by 20 slots each having alength of 0.5 ms. The slots have numbers of 0 to 19. One subframe isconfigured by two continuous slots. In the FDD, 10 subframes are usedfor an uplink transmission and a downlink transmission during 10 ms.

FIG. 2B is a view showing an example of a random access preamble format.

As shown in FIG. 2B, a physical layer random access preamble includes acyclic prefix (CP) having a length of T_(CP) and a sequence part havinga length of T_(SEQ). Parameters are shown in Table 1 and are decided bythe frame structure and the random access configuration. The preambleformat is controlled by the upper layer.

TABLE 1 Preamble format T_(CP) T_(SEQ) 0  3618 · T_(S) 24576 · T_(S) 121024 · T_(S) 24576 · T_(S) 2  6240 · T_(S) 2 · 24576 · T_(S) 3 21024 ·T_(S) 2 · 24576 · T_(S) 4  448 · T_(S)  4096 · T_(S) (Corresponding toonly frame structure type 2.)

With respect to the preamble formats 0 to 3, a maximum of one randomaccess resource exists per subframe. Table 2 shows subframes forallowing a random access preamble transmission in the givenconfiguration. If it is assumed that a timing advance is zero, the startof the random access preamble will be aligned in parallel to the startof an uplink subframe corresponding to a user equipment (terminal). InTable 2, the random access channel has a period of 1 ms to 20 ms.

TABLE 1 PRACH System configuration frame number Subframe number 0 Even 11 Even 4 2 Even 7 3 Any 1 4 Any 4 5 Any 7 6 Any 1, 6 7 Any 2, 7 8 Any 3,8 9 Any 1, 4, 7 10 Any 2, 5, 8 11 Any 3, 6, 9 12 Any 0, 2, 4, 6, 8 13Any 1, 3, 5, 7, 9 14 Any 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 15 Even 9

In the following description, the RACH configuration having the periodof 1 ms will be described. However, the present invention is not limitedto such an RACH period. In addition, since the effect of the presentinvention is further increased when the period is short, the presentinvention may be used only in a specific RACH configuration having ashort period. In addition, although the 3GPP LTE system is used torrconvenience of description, the present invention is not limited tothis. For example, the present invention is applicable to a rangingchannel of the IEEE 802.16 (hereinafter, referred to as 802.16). Inother words, an RACH response of the LTE described in the presentinvention may be analyzed as a ranging response of the 802.16.

FIG. 3A is a view showing a random access response including timeinformation according to an embodiment of the present invention.

In the embodiment of the present invention described in FIG. 3A, since amethod of transmitting a random access response including timeinformation is used, it is possible to prevent the random accessresponse from being erroneously received. In this case, since additionalinformation is further transmitted, signaling overhead may slightlyoccur. For example, as shown in FIG. 3A, when the base station transmitsthe random access response, it is possible to transmit the uplinksubframe number of the time point when the user equipment transmits arandom access request (random access preamble) (hereinafter, the uplinksubframe number of an uplink subframe 0 is denoted by “0”). Like theembodiment described in FIG. 3A, it is assumed that each subframe has alength of 1 ms in a time domain. In addition, it is assumed that an RACHslot for transmitting the random access preamble has a period of 1 ms. Auser equipment 1 may transmit a random access preamble having a randomlyselected sequence number 1 in an uplink subframe 0 (S310). A userequipment 2 may transmit a random access preamble having a sequencenumber 1, which is randomly selected but is identical to the sequencetransmitted by the user equipment 1, in an uplink subframe 1 (S320). Abase station may receive the random access sequence transmitted by theuser equipment 1 in a downlink subframe 3 and then transmit a randomaccess response thereof (S330). This random access response may includeinformation about the sequence number 1 and the uplink subframe 0.Thereafter, the base station may receive the random access sequencetransmitted by the user equipment 2 in a downlink subframe 4 and thentransmit a random access response thereof (S340). This random accessresponse may include information about the sequence number 1 and theuplink subframe 1. The user equipment 1 and the user equipment 2 mayreceive the random access response of the random access preambletransmitted by the user equipment 1 in an uplink subframe 7. Thereafter,the user equipment 1 and the user equipment 2 may check whether theuplink subframe number included in the received random access responseis identical to any one of the uplink subframe numbers of the randomaccess preambles transmitted by the user equipment 1 and the userequipment 2. If the uplink subframe number included in the random accessresponse received by the user equipment 1 is identical to the uplinksubframe number of the random access preamble transmitted by the userequipment 1, it may be determined, that the random access responsereceived by the user equipment 1 is the response of the random accesstransmitted by the user equipment 1. However, if the uplink subframenumber included in the random access response received by the userequipment 1 is not identical to the uplink subframe number of the randomaccess preamble transmitted by the user equipment 1, it may bedetermined that the random access response received by the userequipment 1 is not the response of the random access transmitted by theuser equipment 1. Similarly, if the uplink subframe number included inthe random access response received by the user equipment 2 is identicalto the uplink subframe number of the random access preamble transmittedby the user equipment 2, it may be determined that the random accessresponse received by the user equipment 2 is the response of the randomaccess transmitted by the user equipment 2. However, if the uplinksubframe number included in the random access response received by theuser equipment 2 is not identical to the uplink subframe number of therandom access preamble transmitted by the user equipment 2, it may bedetermined that the random access response received by the userequipment 2 is not the response of the random access transmitted by theuser equipment 2.

In FIG. 3A and the description related to FIG. 3A, a cell radius is notconsidered in order to facilitate the understanding of the problems ofthe technology related to the present invention. However, if the cellradius is actually about 50 km and the propagation speed of anelectromagnetic wave is considered, the random access preambletransmitted by the user equipment 1 in the uplink subframe 0 may reachthe base station in a downlink subframe 0 or a downlink subframe 1, andthe random access preamble transmitted by the user equipment 2 in theuplink subframe 1 may reach the base station in a downlink subframe 1 ora downlink subframe 2. Similarly, a random access response transmittedby the base station in the downlink subframe 1 may reach the userequipment 1 and/or the user equipment 2 in the uplink subframe 1 or anuplink subframe 2 and a random access response transmitted by the basestation in the downlink subframe 2 may reach the user equipment 1 and/orthe user equipment 2 in the uplink subframe 2 or an uplink subframe 3(see FIG. 3B).

FIG. 4 is a flowchart illustrating a method of transmitting, andreceiving, a random access between a user equipment 1, a user equipment2 and a base station, according to another embodiment of the presentinvention.

The user equipment 1 and the user equipment 2 select random accesschannel parameters, such as a PRACH configuration and a preamble format,in steps S410 and S410′, respectively. As the PRACH configuration andthe preamble format, one of the configurations shown in Table 1 andTable 2 may be selected. The user equipment 1 and the user equipment 2may decide the sequence number of the random access preamble to betransmitted and apply it to the preamble, respectively. The randomaccess preamble sequence numbers transmitted by the user equipment 1 andthe user equipment 2 may be identical or different. In this embodiment,it is assumed that the sequence numbers transmitted by the userequipment 1 and the user equipment 2 are identical to “1”. The userequipment 1 and the user equipment extract and store the uplink subframenumbers at time points when the random access preambles are transmitted,in steps S420 and S420′, respectively. The time point when the randomaccess preamble is transmitted by the user equipment 1 may be differentfrom the time point when the random access preamble is transmitted bythe user equipment 2. Hereinafter, the respective uplink subframenumbers stored by the user equipment 1 and the user equipment 2 aredenoted by sf_F_N. In this embodiment, the random access preambles RAP1and RAP2 transmitted by the user equipment 1 and the user equipment 2are transmitted at time points corresponding to the uplink subframenumbers sf_F_N=1 and sf_F_N=2, respectively. The user equipment 1 andthe user equipment 2 transmit the random access preambles in steps S430and S430′, respectively.

If the base station 3 receives the random access preambles (e.g., RAP1and RAP2), the base station 3 extracts the sequence numbers of thereceived, random access preambles and estimates the uplink subframenumbers sf_F_N=j, which might be transmitted by the received randomaccess preambles, in consideration of the cell radius (cell size). Thebase station 3 includes the estimated information in the random accessresponses of the received random access preambles (S440). Thereafter,the base station 3 transmits the random access responses (S450). Thetransmitted random access responses may reach the user equipment 1 andthe user equipment 2. In this embodiment, the base station 3 transmitsthe random access response of the random access preamble transmitted bythe user equipment 1 before transmitting the random access response ofthe random access preamble transmitted by the user equipment 2. The userequipment 1 and the user equipment 2 receive the respective randomaccess responses transmitted in the step S450. The user equipment 1 andthe user equipment 2 extract the uplink subframe numbers included in thereceived random access responses and compare the extracted subframenumbers with the uplink subframe numbers stored in the step S420 (stepS420′), in the steps S460 and S460′. In the user equipment 1, since theuplink subframe number sf_R_N=1 included in the received random accessresponse is identical to the stored uplink subframe number sf_F_N=1 ofthe random access preamble transmitted by the user equipment 1, it maybe determined that the received random access response is the responseof the random access preamble transmitted by the user equipment 1. Inthe user equipment 2, since the uplink subframe number sf_RN=1 includedin the received random access response is different from the storeduplink subframe number sf_F_N=2 of the random access preambletransmitted by the user equipment 2, it may be determined that thereceived random access response is not the response of the random accesspreamble transmitted by the user equipment 2. Each user equipment mayfurther use sequence information included in the received random accessresponse as well as the uplink subframe number included in the receivedrandom access response, in order to check whether the random accessresponse received by each user equipment is the response of the randomaccess preamble transmitted by each user equipment. If both the sequenceinformation and the uplink subframe number included in the random accessresponse received by any user equipment are identical to the sequenceinformation included in the random access preamble transmitted by theuser equipment and the uplink subframe number at the time point when theuser equipment transmits the random access preamble, it may bedetermined that the received random access response is the response ofthe random access preamble transmitted by the user equipment.

FIG. 5A shows the case where each subframe has a length of 1 ms in atime domain and an RACH slot for transmitting a random access preamblehas a period of 2 ms.

A user equipment 1 transmits a random access preamble having a randomlyselected sequence number 1 in an uplink subframe 0 (S510). A userequipment 2 transmits a random access preamble having a sequence number1, which is randomly selected but is identical to the sequencetransmitted by the user equipment 1 in an uplink subframe 2 (S520). Abase station receives the random access sequence transmitted by the userequipment 1 in a downlink subframe 3 and then transmits a random accessresponse thereof (S530). This random access response (S530) includes thesequence number 1 and the uplink subframe number sf_F_N=0 included inthe random access preamble received in the downlink subframe 3, which isestimated by the base station in consideration of a cell radius (cellsize). Thereafter, the base station receives the random access sequencetransmitted by the user equipment 2 in a downlink subframe 5 and thentransmits a random access response thereof (S540). This random accessresponse (S540) may include the sequence number 1 and the uplinksubframe number sf_F_N=2 included in the random access preamble receivedin the downlink subframe 5, which is estimated by the base station inconsideration of a cell radius (cell size).

The embodiment of FIG. 5A is different from the embodiment of FIG. 3A inthat the random access sequence is transmitted only in the uplinksubframe having an even number. That is, the random access sequence istransmitted only in the uplink subframes 0, 2, 4, 6 and 8 which ishatched in FIG. 5A. Accordingly, in order to enable the base station toestimate the uplink subframe numbers so as to represent the numbers bybinary numbers, four signaling bits are necessary. If the originaluplink subframe numbers Original={0, 2, 4, 6, 8} are renumbered toRenumbered={0, 1, 2, 3, 4}, the numbers can be represented using onlythree signaling bits. Thus, it is possible to reduce the number ofsignaling bits. This concept is applicable to the embodiment of FIG. 4.

Although one RACH channel is present per subframe in the presentinvention, this is exemplary for convenience of description and thepresent invention is applicable to the case were several RACH channelsare present per subframe. For example, the RACH channel number and thesubframe number can be signaled on a frequency within a subframe.Alternatively, the numbers may be two-dimensionally allocated, andsignaled in frequency and time domains. An RACH channel may be numberedon a frequency within a subframe and an RACH channel of a next subframemay be then numbered subsequent to that number. In contrast, an RACHchannel is first numbered on a subframe and an RACH channel may be thennumbered on another frequency domain subsequent to that number.

In the invention, the RACH subframe number may be defined in the unit offrames or superframes.

In FIG. 5A and the description related to FIG. 5A, a cell radius is notconsidered in order to facilitate the understanding of the problems ofthe technology related to the present invention. However, if the cellradius is actually about 50 km and the propagation speed of anelectromagnetic wave is considered, the random access preambletransmitted by the user equipment 1 in the uplink subframe 0 may reachthe base station in a downlink subframe 0 or a downlink subframe 1, andthe random access preamble transmitted by the user equipment in theuplink subframe 2 may reach the base station in a downlink subframe 2 ora downlink sublime 3. Similarly, a random access response transmitted bythe base station in the downlink subframe 1 may reach the user equipment1 and/or the user equipment 2 in the uplink subframe 1 or an uplinksubframe 2, and a random access response transmitted by the base stationin the downlink subframe 3 may reach the user equipment 1 and/or theuser equipment 2 in the uplink subframe 3 or an uplink subframe 4 (seeFIG. 5B).

FIG. 6A is a view showing a delayed random access response if an RACHslot has a period of 2 ms, in the embodiment of FIG. 5A.

That is, the random access response of the uplink subframe 0 is delayed.When a base station receives a random access preamble in a downlinksubframe 3 (S610), the base station may not have a resource which willbe transmitted in downlink. This may occur in various cases. Forexample, if a resource is used for a dedicated multicast broadcastsingle frequency network (MBSFN), a unicast downlink resource cannot beallocated. In contrast, although a resource is not used for a specialpurpose, all resources may be used for other control signals and datasignals at a specific time. In this case, the transmission of the randomaccess response may be delayed. In addition, several random accessresponses may be simultaneously transmitted by one resource.Accordingly, time information (that is, delay offset information)related to the delayed time is preferably included in the random accessresponse. As the time information (or the time related information),other information related to the time and/or the subframe number may beused.

In FIG. 6A and the description related to FIG. 6A, a cell radius is notconsidered in order to facilitate the understanding of the problems ofthe technology related to the present invention. However, if the cellradius is actually about 50 km and the propagation speed of anelectromagnetic wave is considered, the random access preambletransmitted by the user equipment 1 in the uplink subframe 0 may reachthe base station in a downlink subframe 0 or a downlink subframe 1, andthe random access preamble transmitted by the user equipment 2 in theuplink subframe 2 may reach the base station in a downlink subframe 2 ora downlink subframe 3. Similarly, a random access response transmittedby the base station in the downlink subframe 3 may reach the userequipment 1 and/or the user equipment 2 in the uplink subframe 3 or anuplink subframe 4 (see FIG. 6B).

FIGS. 7A and 7B are views explaining, renumbering and grouping accordingto another embodiment of the present invention.

Up to now the uplink subframe number or the renumbered uplink subframenumber was used as the time information included in the random accessresponse. However, a grouping method may be used when the uplinksubframe number is renumbered. As the grouping method, a modulooperation and/or various known methods may be used (the modulo operationindicates an operation for obtaining a remainder when a number isdivided by another number). For example, a modulo-4 operation indicatesan operation for obtaining a remainder when any number is divided by 4as a result value. For example, the subframe number may be renumbered soas to be repeated in a period of 10 ms or less. For example, while 4-bitsignaling is necessary if a fifteenth PRACH configuration of Table 2 isused, 2-bit signaling is necessary it the uplink subframe number issubjected to the modulo-4 operation. Application examples may be madeusing various PRACH configurations of Table 2. FIGS. 7A and 7B show oneof these examples. In FIGS. 7A and 7B, in a configuration in which thelength of an uplink subframe is 1 ms and RACH slots are repeated in aperiod of 2 ms, the uplink subframe numbers in which the RACH slots arepresent are renumbered. The uplink subframe numbers are grouped andrepeated by the modulo-4 operation.

FIG. 8 is a flowchart in detail illustrating an internal process of astep S420 of FIG. 4, in which the embodiment of FIG. 7 is applied, tothe embodiment of FIG. 4.

In a step S810, subframes in which an RACH slot is present are detected.In a step S820, numbers are reallocated, to only the uplink subframes inwhich the RACH slot is present. In a step S830, the reallocated numberof an uplink subframe at a time point when a random access will betransmitted is decided. In a step S840, the decided reallocated numberis stored. Although, in this embodiment, the RACH slots are present onlyin even-numbered frames, the RACH slots may be present in any numberedframes. That is, the reallocation of the numbers in the step S830 mayuse the grouping method. In more detail, the modulo operation may beused.

FIG. 9 is a flowchart illustrating a method of transmitting andreceiving a random access request and a random access response accordingto another embodiment of the present invention, that is, a method oftransmitting and receiving a random access between a user equipment 1, auser equipment 2 and a base station.

The user equipment 1 and the user equipment 2 may select random accesschannel parameters such as a PRACH configuration and a preamble formatin steps S910 and S910′, respectively. As the PRACH configuration andthe preamble format, one of the configurations shown in Table 1 andTable 2 may be selected. The user equipment 1 and the user equipment 2decide the sequence numbers of the random access preambles to betransmitted and apply to the random access preambles, respectively. Inthis embodiment, the random access preamble sequence numbers transmittedby the user equipment 1 and the user equipment 2 may be identical ordifferent. The user equipment 1 and the user equipment 2 extract theuplink subframe numbers at time points when the random access preamblesare transmitted and include the extracted uplink subframe numbers in therandom access preambles to be transmuted in steps S920 and S920′,respectively. The time point when the random access preamble istransmitted by the user equipment 1 may be different from the time pointwhen the random access preamble is transmitted by the user equipment 2.Hereinafter, the respective uplink subframe numbers included in therandom access preambles transmitted by the user equipment 1 and the userequipment 2 are denoted by sf_F_N. In this embodiment, the random accesspreambles RAP1 and RAP2 transmitted by the user equipment 1 and the userequipment 2 are transmitted at time points corresponding to the uplinksubframe numbers sf_F_N=1 and sf_F_N=2, respectively. The user equipment1 and the user equipment 2 transmit the random access preambles in stepsS930 and S930′, respectively. In this embodiment, it is assumed thatboth the random access preambles transmitted by the user equipment 1 andthe user equipment 2 have a sequence number 1.

If the base station 3 receives the random access preambles e.g., RAP1and RAP2), the base station 3 may extract the sequence numbers and theuplink subframe number sf_F_N=j included in the received random accesspreambles and include the extracted information in the random accessresponses of the received random access preambles (S940). Hereinafter,the uplink subframe number included in the random access response isdenoted by sf_R_N. Thereafter, the base station 3 transmits the randomaccess response RAR1 (S950). The transmitted random access response RAR1may reach the user equipment 1 and the user equipment 2. In thisembodiment, the base station 3 may transmit the random access responseRAR1 of the random access preamble transmitted by the user equipment 1before transmitting the random access response RAR2 of the random accesspreamble transmitted by the user equipment 2. The user equipment 1 andthe user equipment 2 receive the respective random access responses RAR1transmitted in the step S950. The user equipment 1 and the userequipment 2 extract the uplink subframe number included in the receivedrandom access responses RAR1 and compare the extracted uplink subframenumber with the uplink subframe numbers included in the respectiverandom accesses transmitted by the user equipments, in the steps S960and S960′. In the user equipment 1, since the uplink subframe numbersf_R_N=1 included in the received random access response RAR1 isidentical to the uplink subframe number sf_F_N=1 of the random accesspreamble RAP1 transmitted by the user equipment 1, it may be determinedthat the received random access response RAR1 is the response of therandom access preamble RAP1 transmitted by the user equipment 1. In theuser equipment 2, since the uplink subframe number sf_R_N=1 included inthe received random access response RAR1 is different from the uplinksubframe number sf_F_N=2 of the random access preamble RAP2 transmittedby the user equipment 2, it may be determined that the received randomaccess response RAR1 is nor the response of the random access preambleRAP2 transmitted by the user equipment 2. Each user equipment mayfurther use sequence information included in the received random accessresponse as well as the uplink subframe number included in the receivedrandom access response, in order to check whether the random accessresponse received by each user equipment is the response of the randomaccess preamble transmitted by each user equipment. If both the sequenceinformation and the uplink subframe number included in the random accessresponse received by any user equipment are identical to the sequenceinformation and the uplink subframe number included in the random accesspreamble transmitted by the user equipment, it may be determined thatthe received random access response is the response of the random accesspreamble transmitted by the use equipment.

FIG. 10 is a view in detail showing an internal process of the step S920(S920′) of FIG. 9.

The user equipments 1 and 2 decide the uplink subframe numbers at thetime point when the random access preambles are transmitted. Thereafter,the user equipments 1 and 2 add the uplink subframes numbers decided inthe step S1010 to the preambles to be transmitted, in a step S1020.FIGS. 11, 12 and 13 are views facilitating the understanding of theother embodiments of the present invention, which show the principle ofan ARQ, the principle of a HARQ and a detailed example of a HARQprocess, respectively.

In the other embodiments of the present invention, a user equipmentwaits for a response at a predetermined time period. The user equipmentwhich transmits a random access preamble can previously know a timepoint when a response of the random access preamble transmitted by theuser equipment is transmitted, on the basis of the predetermined timeperiod.

For example, the predetermined time period may be decided in associationwith HARQ timing. The HARQ is a hybrid technology of an ARQ technologyof an MAC layer and a channel coding technology of a physical layer. TheARQ is a closed-loop error correction method based on feedback. If anerror occurs in the physical layer in spite of making an effort tosuppress the occurrence of the error in a transmission by forward errorcorrection (FEC), a packet in which the error occurs is retransmitted bythe ARQ in an RLC layer. As a result, when data is transmitted to theRLC layer in uplink, information may be restored by only packets withoutan error.

FIG. 11 is a view explaining the principle of the ARQ. If an erroroccurs when a packet P₁ transmitted by a transmitter Tx is received by areceiver Rx (S1110), the receiver Rx transmits a negativeacknowledgement (NAK) signal (S1120). The transmitter Tx which receivesthe NAK signal retransmits the same packet P₁ as the packet P₁ in whichthe error occurs upon transmission (S1130). If the receiver Rx confirmsthat an error does not occur in the retransmitted packet, the receiverRx transmits an ACK signal to the transmitter Tx (S1140). Thetransmitter Tx which receives the ACK signal transmits a new packet P₂(S1150).

FIG. 12 is a view explaining the principle of the HARQ. The HARQ isdifferent from the ARQ in that the channel coding of the physical layeris combined to the ARQ. If an error occurs when a receiver Rx receives apacket P_(1A) transmitted by a transmitter Tx (S1210), the receiver Rxtransmits an NAK signal (S1220). The transmitter Tx which receives theNAK signal transmits a packet P_(1B) (S1230). In FIG. 12, the packetP_(1A) and the packet P_(1B) are made of the same information bits, thatis, the same channel encoder input packet P_(1A) and are identical orslightly different. In the HARQ, although an error occurs in the packetP_(1A) which is first transmitted, since the packet P_(1A) has anyinformation amount, the packet P_(1A) is stored without being discardeduntil the retransmitted signal is received and is soft-combined with theretransmitted signal P_(1B) or is demodulated using another method. Amethod of utilizing packets in which errors occur and newlyretransmitted packets includes a chase combining (CC) method and anincremental redundancy (IR) method.

Each user equipment can estimate a random access response location onthe basis of HARQ timing at a time location of the RACH slot transmittedby the user equipment and receive only a downlink signal in a specifictime location section. For example, like FIG. 13 showing the example ofthe HARQ process, if it is assumed that a time consumed for performingthe HARQ process is 1 ms and the number of HARQ processes is 8, a timeconsumed for, at the user equipment, processing a signal transmittedfrom a base station in downlink and, at the base station, processing thesignal transmitted by the user equipment in uplink is 8 ms in FIG. 13,T_(prop) denotes a propagation delay time. A half of a HARQ round triptime or a half of the total number of HARQ processes is consumed forreceiving a response of a transmitted signal excluding the processingtime of the received signal.

The user equipment which attempts random access may wait for a half ofthe HARQ round trip time or a half of the total number of HARQ processesfrom a time point when a random access preamble is transmitted, and waitfor a response within a predetermined time period from a time point whena half of the HARQ round trip time or a half of the total number of HARQprocesses elapses. Alternatively, a method of applying an offset (delayoffset) in consideration of a difference between a data processing timeand a random access processing time may be used. For example, a methodof receiving a downlink signal by the user equipment at a locationseparated from a time determined by the HARQ round trip time or thetotal number of HARQ processes by one subframe. This offset may berepresented by adding or subtracting a predetermined number and may berepresented by a multiple of the number of HARQ processes.

If the RACH having a length of 2 ms or 3 ms is transmitted in the abovemethod, a method of estimating a time for waiting for a response from atime location for a start time location of an RACH slot is possible.Alternatively, a method of estimating a time for waiting for a responsefrom a time location for an end time location of art RACH slot ispossible.

It is possible to prevent each user equipment to erroneously receive aresponse for another user equipment as its response using apredetermined response reception time location. If this method is used,signaling overhead is no longer included in random data in whichoverhead is transmitted and received.

FIG. 14 is a flowchart illustrating a method of transmitting andreceiving a random access between a user equipment 1, a user equipment 2and a base station, according to an embodiment of the present invention.

The user equipment 1 and the user equipment 2 select random accesschannel parameters, such as a PRACH configuration and a preamble format,in steps S1410 and S1410′, respectively. As the PRACH configuration andthe preamble format, one of the configurations shown in Table 1 andTable 2 may be selected. The user equipment 1 and the user equipment 2may decide the sequence numbers of the random access preambles to betransmitted and apply it to the random access preambles, respectively.In this embodiment, the random access preamble sequence numberstransmitted by the user equipment 1 and the user equipment 2 may beidentical or different. The user equipment 1 and the user equipment 2decide default times, in which the random access responses of the randomaccess preambles to be transmitted will be received, and default uplinksubframe sections in advance. The default times or the default uplinksubframe sections may be changed when processing delay occurs in thebase station. This change may be, although described below, performedby, at the base station, transmitting a random access response in astate of including information about a processing delay time whenprocessing delay occurs in the base station. The time point when therandom access preamble is transmitted by the user equipment 1 may bedifferent from the time point when the random access preamble istransmitted by the user equipment 2. In this embodiment, the randomaccess preambles RAP1 and RAP2 transmitted by the user equipment 1 andthe user equipment 2 are transmitted at time points corresponding to theuplink subframe numbers sf_F_N=1 and sf_F_N=2, respectively. The userequipment 1 and the user equipment 2 transmit the random accesspreambles in steps S1430 and S1430′, respectively.

If the base station 3 receives the random access preambles (e.g., RAP1and RAP2), the base station 3 transmits a random access response RAR1 ofthe received random access preambles. At this time, as described abovein association with FIG. 7, if the base station uses all resources forother processes and thus cannot allocate the resources with respect tothe random access request, processing delay may occur when the randomaccess response is transmitted. If such processing delay occurs, thebase station 3 may include information about the processing delay time(timing offset) in the random access response (S1440). Thereafter, thebase station transmits a random access response RAR1 (S1450). Thetransmitted random access response may reach both the user equipment 1and the user equipment 2. In this embodiment, the base station 3transmits the random access response RAR1 of the random access preambletransmitted by the user equipment 1 before transmitting the randomaccess response RAR2 of the random access preamble transmitted by theuser equipment 2. The user equipment 1 and the user equipment 2 receivethe respective random access responses transmitted in the steps S1460and S1460′. The user equipment 1 and the user equipment 2 check whetherthe received random access responses are received at the default timesset in the steps S1460 and S1460′, respectively. Hereinafter, the stepS1460 of the user equipment 1 will be described.

It is assumed that the received random access response is received atthe default time set by the user equipment 1. At this time, the receivedrandom access response may be or may not be the response of the randomaccess preamble transmitted by the user equipment 1. If the offsetincluded in the received random access response is 0 (zero), it isindicated that the processing delay does not occur in the base station3. Accordingly, it may be determined that the random access responsereceived at the default time set by the user equipment 1 is the responseof the random access preamble transmitted by the user equipment 1. Incontrast, if the offset included in the received random access responseis not 0 (zero), it is indicated that the processing delay occurs in thebase station. Accordingly, it may be determined that the random accessresponse received at the default time set by the user equipment 1 is notthe response of the random access preamble transmitted by the userequipment 1.

Subsequently, the step S1460 of the user equipment 1 will be described.It is assumed that the received random access response is not receivedat the default time set by the user equipment 1. At this time, thereceived random access response may be or may not be the response of therandom access preamble transmitted by the user equipment 1. If theoffset included in the received random access response is 0 (zero), itis indicated that the processing delay does not occur in the basestation 3. Accordingly, the user equipment 1 should receive the randomaccess response at the default time set by the user equipment 1. Thus,it may be determined that the received random access response is not theresponse of the random access preamble transmitted by the user equipment1. In contrast, if the offset included in the received random accessresponse is not 0 (zero), it is indicated that the processing delayoccurs in the base station. Accordingly, it may be determined that therandom access response received at the default time set by the userequipment 1 is the response of the random access preamble transmitted bythe user equipment 1. It is assumed that the user equipment 1 receivesthe random access response after j sections (or the number of subframesor the time) from a time decided in the step S1420. At this time, theoffset included in the received random access response corresponds tothe j sections, it is determined that the received random accessresponse is the response of the random access preamble transmitted bythe user equipment 1. In contrast, if the offset included in thereceived random access response does not correspond to the j sections,it is determined that the received random access response is not theresponse of the random access preamble transmitted by the user equipment1.

The above-described embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponent and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toanother. Some components or characteristics of any embodiment may alsobe included in other embodiments, or may be replaced with those of theother embodiments as necessary. It will be apparent to those skilled inthe art that unrelated claims are combined so as to configureembodiments or are included in new claims by amendments after anapplication.

The above-mentioned embodiments of the present invention are disclosedon the basis of a data communication relationship between a base stationand a mobile station. In this case, the base station is used as aterminal node of a network via which the base station can directlycommunicate with the mobile station. Specific operations to be conductedby the base station in the present invention may also be conducted by anupper node of the base station as necessary. In other words, it will beobvious to those skilled in the art that various operations for enablingthe base station to communicate with the mobile station in a networkcomposed of several network nodes including the base station will beconducted by the base station or other network nodes other than the basestation. The term “Base Station” may be replaced with a fixed station,Node-B, eNode-B (eNB), or an access point as necessary. The term “mobilestation” may also be replaced with a user equipment (UE), a mobilestation (MS) or a mobile subscriber station (MSS) as necessary.

The embodiments of the present invention can be implemented by a varietyof means, for example, hardware, firmware, software, or a combination ofthem. In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The present invention is applicable to a wireless mobile communicationapparatuses.

What is claimed is:
 1. A method for performing a random access procedureby a user equipment (UE), the method comprising: transmitting a randomaccess preamble to a base station; determining a time period forreceiving a random access response responsive to the random accesspreamble; and receiving the random access response from the base stationwithin the time period, wherein the time period starts at a time pointafter an end time of transmitting the random access preamble, and asubframe number corresponding, to the time point is obtained by addingan offset to a subframe number corresponding to the end time oftransmitting, the random access preamble, and the offset equals three.2. The method of claim 1, wherein the offset is determined based on aprocessing time of a hybrid automatic repeat request (HARQ) process anda processing, time of the random access procedure.
 3. The method ofclaim 1, wherein the offset is determined by subtracting one subframefrom a half of a round trip time of a hybrid automatic repeat request(HARQ) process, the round trip time of the HARQ process corresponding toeight subframes.
 4. A method for performing a random access procedure bya base station, the method comprising: receiving a random accesspreamble from a user equipment (UE); determining an end time in whichtransmitting the random access preamble was terminated by the UE;generating a random access response in response to the random accesspreamble; and transmitting the random access response to the UE withinthe time period, wherein the time period starts at a time point afterthe end time in which transmitting the random access preamble wasterminated by the UE, and a subframe number corresponding to the timepoint is obtained by adding an offset to a subframe number correspondingto the end time, and the offset equals three.
 5. The method of claim 4,wherein the offset is determined based on a processing time of a hybridautomatic repeat request (HARQ) process and a processing time of therandom access procedure.
 6. The method of claim 4, wherein the offset isdetermined by subtracting one subframe from a half of a round trip timeof a hybrid automatic repeat request (HARQ) process, the round trip timeof the HARQ process corresponding to eight subframes.
 7. A userequipment (UE) to perform a random access procedure, the UE comprising:a transmitter to transmit a random access preamble to a base station; aprocessor configured to determine a time period for receiving a randomaccess response responsive to the random access preamble; and a receiverto receive the random access response from the base station within thetime period, wherein the time period starts at a time point after an endtime of transmitting the random access preamble, and a subframe numbercorresponding to the time point is obtained by adding an offset to asubframe number corresponding to the end time of transmitting the randomaccess preamble, and the offset equals three.
 8. The user equipment ofclaim 7, wherein the offset is determined based on a processing time ofa hybrid automatic repeat request (HARQ) process and as processing timeof the random access procedure.
 9. The user equipment of claim 7,wherein the offset is determined by subtracting one subframe from a halfof a round trip time of a hybrid automatic repeat request (HARQ)process, the round trip time of the HARQ process corresponding to eightsubframes.
 10. A base station to perform a random access procedure, thebase station comprising: a receiver to receive a random access preamblefrom a user equipment (UE); a processor configured to determine an endtime in which transmitting the random access preamble was terminated bythe UE, and to generate a random access response in response to therandom access preamble; and a transmitter to transmit the random accessresponse to the UE within a time period wherein the time period startsat a time point after the end time in which transmitting the randomaccess preamble was terminated by the UE, and a subframe numbercorresponding to the time point is obtained by adding an offset to asubframe lumber corresponding to the end time, and the offset equalsthree.
 11. The base station of claim 10, wherein the round trip time ofthe HARQ process corresponds to eight subframes and the offsetcorresponds to one subframe.
 12. The base station of claim 10, whereinthe number equals three.
 13. The base station of claim 10, wherein thetransmission of the random access preamble ends in the first subframe.14. The base station of claim 10, wherein the processor is configured todetermine length of the time period in which the UE monitors the randomaccess response.